The invention is directed to an access door of the type that is used on an enclosure for a chute or conveyor of the type for moving grain, minerals, coal or the like. These are also sometimes called inspection doors or dust control doors. The access door (or inspection door) is provided on the cover of the chute or conveyor to permit inspection of the conveyor belt or other equipment without having to remove panels of the housing. The door is hinged onto a frame that is welded or bolted onto the cover panel, and is designed to seal against a gasket to keep the pulverized materials and dust from escaping. There is a problem in the dust containment, in that dust tends to accumulate on horizontal ledges of the frame or on the horizontal flanges of the door. In some attempted improvements, the coaming or closure flange around the opening in the frame has been angled so that a flat level ledge is avoided. However, these angled flanges or coamings have resulted in weakening of the structure because the door seal or gasket bears against the edge of the sealing flange at an angle, which eventually bends it out of alignment.